Electrically-driven tool



A ril 29 S. D. BLACK ET AL ELECTRICALLY DRI EN TOOL Filed June 14 1920 I I I l I I an uewfoz Petent'c'd Apr. 29, 1924.

UNITED STATES PATENT OFFICE.

SAMUEL DUNCAN BLACK AND'ALONZO GALLOWAY DECKER, 0F BALTIMORE, MARY LAND, ASSIGNORS, BY MESNE ASSIGNMENTS, TO THE MARYLAND TRUST COM- PANY, TRUSTEE, A- CORPORATION OF MARYLAND.

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To all 'whom it'may concern:

Be it known that we, SAMUEL DUNCAN BLACK and ALONZO GALLOWAY DECKER, citizens of the United States of America, and residents of Baltimore County, State of Maryland, have invented certain new and useful Improvements in Electrically-Driven Tools, of which the following is a specifics tion.

electrically driven tool, of" the type described m United States Patent No. 1,245,860, and particularly to the controlling device or switch which is a feature of that atent. A difliculty with that type of switc i. e., the rotary switch, was that incident to maintaining a uniform and sufiiciently close contact between the rotar contact block and the switch arm or eaves;

or loss of tension in one of the spring eaves would cause the contact of t at eaf with the block to become imper' feet, resultin in arcing and consequent deterioration o the contact by burning. As already suggested, this loss of tension in'the spring leaves is apt to be more pronounced in one member than in the other and conversely it was diflicult to adjust the two s ring leaves to get equal tension and equal 0 oseness of contact on both sides of the block. This diliicultty) has been overcome in the present instance y mounting the spring arms or leaves of the switch on a support which is pivoted to swing freely, perm1tting the spring arms to adjust themselves, equalizing the contact pressure of the two arms on-the respective s1des of the rotary contact block.

Another feature of the invention is found in the construction ofthe switch whereby the rotary contact block ma when burnt out, be conveniently remove without necessitating the employment special tools.

The invention further resides in the ar ran ement of the details of the contact bloc in such a manner as to ive increased economy in production and e ciency of operation. I

In the accom anyin drawings we have illustrated an e ectrica 1y driven tool and parts thereof, embodying the features of our invention in its preferred form.

Bendin This invention relates to an improved,

and replaced the invention, the lane of section being parallel to the axis o the tool.

Figure 2 is a section on the line 22 of Figure 1, at right angles to the plane of Figure 1 and on the axis of the contact block.

Fi re 3 is a section on the line -3--3 of Figure 2, illustrating the details of the contact block. 1

Figure 4 is a plan of the switch-box. Figure 5 is an elevation of the tool. Referring to the drawings by numerals, each of which is used to indicate the same or similar parts in the difierent figures; the tool as indicated consists of a suitable frame or ,casing (1), in which is mounted an electric motor (2), with gearing or suitable connections (3), to a tool chuck (4). The tool is supported and guided b a handle or pistol grip (b5) and controllecl by a switch (6) actuated a trigger (7). Having particular re erence to Figures, 1 to 4, illustrating the details of the switch to which the invention particularly relates, the switch consists of arotary contact block (10) and two springcontact arms (9 and 11) mounted on an insulating carrier block (12), to the opposite sides of which the contact arms (9 and 11) are secured by rivets (13) or other suitable means. The contact arm- (11) is connected to an insulated wire (14) leading from a source of electric current, and the contact arm (9) is similarly connected by. a wire (15) to the motor (2).

-Connected to a screw and hook-like binding post (40) ,the wire 14 leads to a suitable source of electricity and the op osite contact arm carries a second similar binding post (41) from which a wire 15 leads to the motor. The return or wire (17) leading from the motor is supported on the contact I block by a screw or suitable attachment (42) The return, ound, or negative connection 17 is joine to the o posite terminal of the motor so that when t e two switch arms (9 and 11) are closed or electrically connected to the contact block (10) the motor is in circuit, and when they are disconnected by rotation of the block to a position in which they engage the non conducting portions of the present instance these electrically-coir ducting faces (1616) and the connecting means therefor, indicated by reference character (46) are formed and consist of a U- shaped strap of metal, clasping and enclos' ing thehard rubber block (18) which forms the body of the contact block, the two legs of the U forming the conducting, contacting surfaces (HS-16) and the crossarm of the U forming the connection (46) which is led across one of the axial ends of the block (18) and preferably seated in a suitable groove or depression therein.

Preferably the block is cut away at 47 below the edges of the contacting surfaces (16-16) to prevent arcing at this point when the terminals are disconnected.

In the form of the invention shown the rubber is cut away to form an insulating hub portion (19) concentric with the axis at the end of the block occupied by the cross arm of the U, and the cross-arm is apertured to admit the hub which is also passed through an insulating washer (20') completely separating and insulating the contacting portions '16 and 46) of the contact block from the metallic casing or box (1) in which it is mounted.

The manner of mounting the contact block in the casing is an important structural detail lending to economy of production and particularly to convenience in replacing the contact members if burned or otherwise destroyed. The casing is provided with two abutments (21 and 22). The frame (2-2) on one side is pierced by a small aperture (24) of circular cross-section and of the diameter of the small end of the shaft (23) as hereinafter described. The opposite side (22) is pierced. in alignment with this aperture (2st), with an aperture (25) of considerably greater diameter. and this aperture is enlarged adjacent the outer surface of the boX or casing, forming a counter-sink (26). The shaft- (27) of the carrier block (10) is mounted in these aligned openings or apertures (24 and 25). This shaft is of square or angular cross-section as to its intermediate portion (28). so as to provide a non-rotating connection with the block (10), which is mounted on and has a square or angular aperture to fit the shaft. A ratchet (29), which is likewise provided with a square, central. axial aperture, is mounted on the same shaft side of the contact block. The

ends of the shaft (23 and 80) are round, to give a rotary engagement with the corresponding openings (24 and 25), and the small end (23) of the shaft extends outward beyond the surface of the casing and is provided with a cotter-pin (31), to prevent accidental withdrawal of the shaft. The opposite end of the shaft is enlarged at to lit the enlarged opening (25), and provided with a head (82), engaging and seated in the counter-sink (26). On the form shown the enlarged end (30) is marked with an arrow or pointer which in conjunction with suitable markings on the frame indicates the on and off position of the switch. The rotary parts (10 and 29) need not be otherwise fastened to the shaft, i. e., by .pinning or keying, but are merely slipped over the shaft, so that if it becomes necessary to replace these members, to remove them the operator has only to withdraw the cotterpin (31) and slip out the shaft by pressing on the protruding end, causing the head to project, when it may be withdrawn releasing the contact block and ratchet, making the replacement of the contact block when necessary a simple operation requiring no special tools and occupying only two or three minutes time.

In the preferred form the wires or cable leading to the source of electricity are introduced thru a covered aperture or split. The boss (51), the upper half or cover of which is removable for convenience in introducing the cable. It is held by screws (53) by which the cable is clamped. This clamping prevents straining or pulling loose of the connections.

As already pointed out. some difficulty has been encountered in connection with such switches, owing to the unevenness of contact of the arms (9 and 11) with the block (10) due to one or both of the arms being more or less bent out of position and the difiiculty of giving them equal tension. In the present instance we have succeeded in equalizing the pressure of these arms by pivoting the insulating carrier (12) on which they are mounted, so that it swings freely about a suitable shaft (33). Under these circunr stances it is onlv necessary to arrange the spring arms so that they are spaced at their ends by a distance somewhat less than the dimension of the contact block. and the pivotal mounting of the carrier equalizes the tension. In case the closeness of contact becomes insufiicient it is only necessary to bend the arms together, when the equalizing effect takes care of the question of individual adjustment.

To rotate the contact block step by step to on and off position. we have provided a trigger lever (34). as in the aforementioned patent, the lever being pivoted in the frame or casing at 35 and extending well onward to the level of the ratchet (29). This trigger lever carries pivoted at its upper end a pawl (36), and both the pawl and the trigger are controlled by a spring (37). When ger and pawls to prevent the escape of the pawls to an inoperative position.

Presuming that theiblock has been turned into contacting position, the trigger having been withdrawn by the spring, it is turned into off position by a second pressure on the trigger, engaging the next tooth and turning the block through a second arc of approximately 90. a

We have thus described an electrically driven tool and the controlling means therefor, embodying our invention in its preferred form, specifically and in detail, in order that the nature and operation of the invention may be clearly understood to those skilled in the art; however, the specific terms herein are used descriptively rather than in a limiting sense, the scope of the invention being defined in the clalms.

What we claim and desire to secure by Letters Patent is:

1. In an electrically driven tool means for starting and stopping the tool comprising a rotary switch-block; spring-controlled contactarms engaging opposite faces of the block; and a ivotally mounted insulating carrier for said arms. 1

2. In an electrically driven'tool means for starting and stopping the tool comprising a rotary contact block, having a plurality of conducting faces and means electrically connecting the same; spring contact 'arms adapted to engage said conducting faces in the closed position of the contact block; and

a non-conducting carr er for said arms, the carrier being pivotally mounted to-equalize the contact pressure of the arms. v

3. In a portable, electrically driven tool means for starting and stopping the tool comprising'a rotary contact block, havin a plurality of conducting contact faces with means electrically connecting the same; a trigger-like lever and means whereby the trigger leverrotates the contact block step by step as it is pressed and released; springactuated contact arms engaging said contact faces in the closed position of the contact block; and a pivotally mounted, non-conducting carrier for said contact arms whereby the contact pressure is equalized.

4. A switch for an electrically driven tool, consisting of a rotary block of insulating material having opposite, conducting, contacting surfaces and a ratchet member, both' having axial openings of angular cross-section; a switch-box h'aving opposite bearings, one of said bearings being enlarged; a. shaft having an enlarged journal to fit said enlarged bearing; a portion of angular crosssection to fit the opening in the block and ratchet; and a smaller journal portion to fit the opposite bearing, the shaft being of such length as to rovide a projecting end which is transverse y apertured to receive a pin, to prevent withdrawal of the shaft.

5. In an electrically driven tool means for starting and stopping the tool comprisin a rotary switchblock; spring-controlle contact arms engaging opposite faces of the block; an insulating carrier for said arms, and a trigger switch with a pawl engaging the contact block, the carrier acting as a stop for the trigger and awl.

6. In an electrica ly driven. tool means for starting and stopping the tool comprising a trigger switch mounted on a pivot pin seated in the body of the tool frame; a shaft to which the switch is secured; indicating means on the tool frame and co-operating means on the shaft end to indicate the on and off positions of the switch.

Signed by us at Towson, 6th day of May, 1920.

SAMUEL DUNCAN BLACK. ALONZO GALLOWAY DECKER. Witnesses:

PORTER H. FLAUTT, WALTER S'rUMPra Maryland, this 

